1. Field of the Invention
The present invention is related to a video signal processing method and apparatus, and more particularly to a deinterlacing method and apparatus for a digital motion picture.
2. Description of the Prior Art
Motion video pictures, based on the sequence of images contained therein, can be represented by using two different ways: progressive and interlaced techniques. The essential difference between the two techniques lies in the sampling timing of scan lines.
With progressive video, all of the pixels (picture elements) constituting a frame (i.e. one video image snapshot within the sequence of video images) of a video image are sampled at the same time. While with interlaced video, alternate lines of the video image are sampled at alternate time. The captured video image using the interlaced video technique results in the creation of two half-frames, referred to as “fields,” which together constitute a single frame in the video sequence. One field is commonly referred to as an even field, and the other field is commonly referred to as an odd field. These two fields together constitute a single frame in a video sequence and generally include the same number of scan lines respectively. Conventional televisions and video recorders are example devices that manipulate image sequences using the interlaced technique, while modern computer monitors and some DVD players are devices that manipulate image sequences using the progressive technique.
In practice, some applications require that interlaced video image sequences be processed and displayed using a device that is configured to handle only progressive image sequences. These applications therefore require that the image sequence be converted from interlaced format to progressive format. This process is typically referred to as “deinterlacing”. A deinterlacing method for a digital motion picture generally tries to interpolate all values of new pixels lying in new scan lines between all adjacent scan lines in the original field (either even or odd) to get a new field. These new pixels, new scan lines and the new field will be hereinafter referred to as the predicted pixels, the predicted scan lines and the predicted field respectively. To determine the values of the predicted pixels, it typically determines in advance that each predicted pixel is located on a moving object (with dynamic pixels) or on a still object (with static pixels). When a predicted pixel is located on a moving object, a method called Bob is usually applied to interpolate the value of the predicted pixel by referencing the values of one or more spatially adjacent pixels in the same original field. When the predicted pixel is located on a still object, a method called Weave is usually applied to interpolate the value of the predicted pixel by collectively referencing the values of pixels in fields with adjacent temporal sequences. As all the predicted pixels, and thus all the predicted scan lines, on the predicted field are determined, the predicted field can be combined with an original field to form a complete non-interlaced (or progressive) frame. It is also noted that, if the original field to be combined with is an even (respectively odd) field, then the predicted field is an odd (respectively even) field.
FIG. 1 shows a block diagram of a conventional deinterlacing apparatus 100 for a digital motion picture, in which the Bob/Weave detection unit 120 uses a threshold value and the relationship between pixel values of the previous field (scan lines therein are stored in the scan line buffer 110) and the current field (stored in the video frame buffer 900) to determine that the predicted pixels are dynamic or static. Such design providing only one threshold value does not take into account the case that a scene may contain artificial lines (such as the lines constructing an artificial scoreboard for a ball game), and fails to provide any detection mechanism for selecting either a Bob or a Weave manner in advance, therefore the overall deinterlacing performance is limited for dynamic motion pictures. For example, due to the difficulty of being correctly detected by using only one threshold value, some artificial horizontal lines in a scene tends to be misjudged as points lying on a dynamic object and thus the associated predicted scan lines will be computed based on a dynamic manner, which generally causes some horizontal lines disappearing in the predicted field.
Other deinterlacing methods or apparatuses for a digital motion picture have been provided. For example, U.S. Pat. No. 6,414,719 provided methods and apparatus for interlace to progressive conversion by using a median filter and alleged that it is capable of obtaining interpolated fields more approximate to the original image. However, the operation of such methods is so complicated that it will generally occupy more system resources, such as memory space and computation time.
In view of the shortcomings of the prior technology mentioned above, there is a need to provide an improved deinterlacing method and apparatus for a digital motion picture to resolve problems such as the disappearing of artificial horizontal lines, bad performance on motion pictures, and occupying too many system resources.